Vibrating clutches

Do all clutches vibrate? My bike and a friend's car vibrate noticeably
while slipping. I know that the two types of clutches are different, and
for the bike case, if the plates are out of round, this will happen. I was
wondering if this was a common thing or if this happens after the vehicle
has been out and about for a while.

 

No, not if they are balanced and properly adjusted, with all pressure
plate bolts tightened an equal amount.

The difference is that motorcyle clutches are usually oil-cooled so
they can be slipped without glazing the fiber plates, and the smaller
diameter
of a motorcycle clutch makes it possible for the clutch to be spun up
to as high as 20K RPM without flying apart.

I cannot imagine a clutch plate somehow wearing "out of round". I can
imagine uneven wear on one side of a fiber plate, making it a little
wedge-shaped, though, and I can imagine the steel plates warping.

I never knew that motorcycles or cars had any problem coming out of
the garage ;-)

But, what you are describing as "vibration" may be what the Brits call
clutch "judder". Judder is noticeable when you release the clutch
pedal or clutch lever in order to start out smoothly.

If the clutch judders, the vehicle starts to move in jerks.

Judder is caused by uneven engagement of a clutch, and is generally
caused by improper adjustment of the bolts in the pressure plate. A
car clutch would have three adjustable bolts to make the pressure
plate push evenly against the friction plate and the friction plate
would push against the flywheel surface at all points at the same time
and the car would start off smoothly.

Japanese motorcycles don't have adjustable bolts in the pressure
plate, but old Triumphs had three bolts to adjust, and Harleys had
them too.

But when you install the 4, 5, or 6 bolts holding the pressure plate
on a Japanese motorcycle, you just normally go ahead and tighten them
all the way.

Even though the manual may specify a torque for the pressure plate
bolts, I don't recommend using a torque wrench on oily bolts, I always
tighten them by hand to avoid breaking them.

Even though the repair manuals specify tightening the pressure plate
bolts all the way, it is not impossible for the pressure plate to be
out of adjustment if some of the parts of the center hub are are worn
or damaged.

My GS-1100 had a problem with clutch slip and a friend advised me to
buy a set of heavy duty clutch springs. When I removed the old
springs, I discovered that some aluminum spacers on the pressure plate
bolts were very worn, and some springs were not preloaded as much as
other springs.

The typical design of a Yamaha, Suzuki, or Kawasaki clutch lets you
get at the 4, 5, or 6 pressure plate bolts easily and see exactly what
is going on.

But Honda engineers seem to have been reading a Dr. Seuss book when
they designed their "hillside snee" clutch.

The "hillside snee" was an animal that grazed on the side of a hill
and its downhill legs were longer than its uphill legs. If frightened
by something attacking it from the front, the hillside snee could only
escape by jumping into its own mouth and turning itself inside out...

The Honda clutch is designed "inside out". Honda put the pressure
plate *inside* the clutch basket so the release mechanism could *pull*
on it from the right side of the motorcycle, instead of *pushing* on
it from the left side by means of a pushrod going through the
transmission mainshaft...

 

Only if it's mounted on the end of the crank. Clutches are geared down
from crankshaft speed.

 

Usually by the primary gear ratio in modern Japanese bikes, as the outer
rim of the clutch basket is machined into being one of the primary gears.

-gc

 

Wops. That's what I meant. My CBR's old fibers were wedged (could see the
indentations flat on one side but not the other), but I couldn't
tell/measure anything on the steels.

I broke one of the 4 clutch spring bolts when I replaced the clutch fibers
last spring. I replaced it with one from Lowe's. Seems to work fine. It
was during tightening that it snapped off. Didn't have a torque wrench, but
at 135lbs, I'm not known for having ham-fisted methods.

I looked for signs of wear but didn't really find any.

It took a while for me to get my head around that diagram, but I did finally
get it.

 

If there is anything at all different about that bolt, it may be
causing problems with the alignment of the pressure plate, and that
may cause abnormal fiber plate wear.

Hardware store bolts are often threaded all the way, or the length of
the threaded part is different from the length of the threads on the
bolts that the motorcycle manufacturer has made specially for their
own designs.

If the manufacturer of the clutch intended the bolt to be threaded
into the clutch basket until it stopped,
a bolt that's threaded all the way may cause pressure plate alignment
problems because it threads too far into the bolt hole.

And, the motorcycle manufacturer will generally specify a high
strength bolt for critical applications.

When you look at the head of a utility grade metric bolt, it won't
have a number on it. But the high strength bolts do have numbers. The
Japanese didn't put numbers like "6" or "8" on the heads of bolts for
good luck.

Never substitute a utility grade bolt for a high strength application.

The three high strength allen bolts that held the starter clutch to
the back of the alternator rotor snapped on my Suzuki, and the parts
department at the local $tealer$hip didn't have the right grade bolt.

The parts weenie found some lower strength bolts that were the right
thread, so I tried to use them.

Needless to say, I had to do the job all over again when the weaker
bolts broke.